Along with recent improvement in the performance of motorcar engines, there is a need for an oil ring used in an internal combustion engine which has achieved a satisfactory reduction in the amount of oil consumption. Accordingly, twists have been added to the shape and the like of an oil ring. For example, there is available an oil ring characterized by a shape in vertical cross-section along a sliding direction of at least one of an upper rail and a lower rail of an oil ring main body.
For example, Patent Literature 1 (Japanese Patent No. 3801250) discloses a two-piece combined internal combustion engine oil ring which reduces the amount of lubricating oil consumption by inhibiting the oil-scraping-up action during a piston upstroke or amplifying the oil-scraping action. More specifically, Patent Literature 1 discloses an oil ring including one rail 11 projecting at a center portion of an outer peripheral surface of an oil ring main body 10, the outer peripheral shape in cross-section of a peak portion of the rail 11 including a contact surface 14 in peripheral contact with and parallel to a cylinder inner peripheral surface 40 and a tapered surface 15 arranged on the upper side so as to be continuous with the contact surface 14 and increasing a ring diameter downward or including one rail in which a rail peak portion has a contact surface 16 parallel to the cylinder inner peripheral surface 40, the contact surface having a width of 0.15 to 0.3 mm.
Patent Literature 2 (National Publication of International Patent Application No. 2003-520931) discloses an oil-scraper piston ring (1) having at least one tapered flange (2, 3) covered with a wear-resistant coating (5). More specifically, Patent Literature 2 discloses an oil-scraper piston ring including at least one tapered flange (2, 3) having the wear-resistant coating (5), wherein in a region of the tapered ring plane of the flange (2, 3), a radial elevation (6) is provided so as to include the wear-resistant coating (5) and have a radial height (t) and an axial width (h5′) that can be determined in advance.